1. Technical Field
The present invention relates to an optical switch which can be applied to an optical signal communication system.
2. Description of Related Art
The fiber-optic communication technique is currently the optimal technique in the wired communication technology and which has been broadly applied to backbone network systems. The transmission medium (i.e., optical fiber) adopted in the fiber-optic communication technique has such characteristics as low transmission loss, extra broad bandwidth, free of electromagnetic interference, small volume, light weight, and high security. Each communication node in a fiber-optic communication network requires an uplink path and a downlink path for transmitting and receiving information, so as to achieve bi-directional information transmission. Generally, the uplink path and the downlink path respectively transmit data on the different optical fiber path. If a working optical fiber path is broken, the system switches the channel-fault optical signals to a corresponding protection optical fiber path according to a protection mechanism. Due to the limitation in the switching states of conventional optical switches, a plurality of fiber-optic protection paths has to be implemented in a fiber-optic communication system in order to maintain a good data transmission performance of the system.
In order to reduce the cost of a fiber-optic communication network and increase the flexibility of the network design, techniques for improving the switching states of an optical switch and accordingly reducing the number of fiber-optic paths implemented between communication nodes have been provided. FIG. 1 is a diagram illustrating the switching states of a conventional optical switch. Referring to FIG. 1, an optical switch is disclosed in U.S. Pat. No. 5,724,165. The optical switch 90 is a 2×2 optical switch and which has two input terminals 104 and 108 and two output terminals 106 and 110. The optical switch 90 has two switching states, namely, the bar state as shown in FIG. 1(a) and the cross state as shown in FIG. 1(b). When the optical switch 90 is in the bar state as shown in FIG. 1(a), an optical signal is transmitted from the input terminal 104 to the output terminal 106 through the optical path 100, and contrarily, the optical signal can be transmitted in a reverse direction from the output terminal 110 to the input terminal 108 through the optical path 102, as indicated by the arrows 112 and 118. The optical signal may also be transmitted through the optical paths as indicated by the arrows 114 and 116.
When the optical switch 90 is in the cross state as shown in FIG. 1(b), the optical signal can be transmitted from the input terminal 104 to the output terminal 110 through the optical path 102, as indicated by the arrow 112, and contrarily, the optical signal can also be transmitted in the reverse direction from the output terminal 106 to the input terminal 108 through the optical path 100, as indicated by the arrow 116. The optical signal may also be transmitted through the optical paths as indicated by the arrows 114 and 118. Bi-directional optical signals can be simultaneously transmitted on the same optical path in an optical switch, and this is referred to as the reciprocal attribute of an optical switch.
FIG. 2 is a diagram illustrating the switching states of another conventional optical switch. Referring to FIG. 2, another optical switch 120 is disclosed in U.S. Pat. No. 6,594,068. The optical switch 120 has two switching states for transmitting optical signals through the unidirectional optical paths 122 and 124, as shown in FIG. 2(a) and FIG. 2(b). However, bi-directional optical signals cannot be transmitted on the same optical path in the optical switch 120, and this is referred to as the non-reciprocal attribute of an optical switch.
The switching states of an optical switch would determine the actual implementation of a fiber-optic network system. Thus, the more switching states an optical switch has, the more simplified the disposition of the fiber-optic network system is, or the more flexible it is to design and maintain the fiber-optic network system.